A Numerical Study on the Impact of E x B Drift on the Vertical Distribution of the Plasma Density Over the Geomagnetic Equatorial Ionospheric Region

Using an in-house developed Quasi Two-Dimensional (QTD) physics-based ionospheric model, the impact of E x B drift velocity on the vertical distribution of the electron density over the equatorial latitude has been investigated. The vertical drift measurements from (a) drift analysis software of Digisonde (b) derived from Digisonde ionograms (c) calculated from the Scherliess-Fejer (SF) model, and (d) obtained from the magnetometer Delta H measurements have been used in this study. Four quiet days in a low solar activity year, representing four seasons of the year 2010, have been chosen for the study. The model-derived electron density profiles using the vertical drifts from all four methods matched well with the Digisonde observation below similar to 150 km at all the Local Times (LTs) for all 4 days. However, since the Digisonde-derived drifts were very low, centered mostly around zero, it led to the overestimation/underestimation of the F-region peak plasma density (nmF2)/height (hmF2). The model simulated electron density profiles using the SF model, and Delta H derived vertical drifts showed good agreement with the observation up to an altitude of similar to 350 km. The study showed that vertical drift is a factor that controls the nmF2 trough around noon over the equatorial latitude. It is seen that plasma diffusion occurs only beyond an altitude of 350 km, while the range of altitudes between 320 and 350 km acts as the "diffusion threshold height." This finding has significant implications for understanding plasma dynamics in the equatorial ionosphere. The present study employed a quasi-two-dimensional theoretical ionospheric model to investigate the impact of vertical drift on the electron density distribution over the equatorial ionosphere. Utilizing vertical drift values derived from Digisonde, Scherliess-Fejer (SF) model calculations, and magnetometer readings, the model was simulated for four distinct days of 2010 representing the four seasons of the year. The electron density profiles generated using all four techniques exhibited a close match to the observed values for all 4 days. However, when very low Digisonde-derived drifts were employed, an overestimation of the F-region density and an underestimation of peak F-region plasma density heights were observed. The study demonstrated that the model-simulated electron density profiles, generated using the SF model and magnetometer-derived vertical drifts, exhibited excellent agreement with the observed profiles at altitudes up to approximately 350 km. Similar variations of the calculated and observed nmF2 values led to the conclusion that vertical drift is a crucial factor in controlling the equatorial noon-time nmF2 trough. Furthermore, the study revealed that plasma diffusion occurred only beyond an altitude of 350 km as the altitude range of 320-350 km acts like a "diffusion threshold height." This paper studies the impact of vertical drift on the vertical distribution of the electron density The plasma vertical drift plays an important role in the noon time nmF2 trough The altitude range 320-350 km can be called as the plasma "diffusion threshold height"